Intrinsic-Dipole-Regulated Carrier Lifetimes in Five-Atomic-Layer Janus Group-III Chalcogenides for Photovoltaic Applications

The intrinsic out-of-plane polarity of two-dimensional (2D) Janus materials provides a natural route to regulate photogenerated carrier dynamics. Here, we study electronic structures, stability, and carrier recombination dynamics of five-atomic-layer Janus group-III chalcogenide monolayers with chemical formulas MNS₃, MNSSe₂, and MNSTe₂, where M and N represent In, Ga, and Al. Strongly tunable carrier lifetimes have been found in these Janus monolayers. After structural stability screening, the carrier recombination time varies from 0.27 ns in InGaSTe₂ to 1272.8 ns in InAlS3, showing a change over more than four orders of magnitude. Moreover, the maximum photocurrent of InAlS₃ reaches 4.13 a₀²/photon, highlighting its potential for high-efficiency photovoltaic applications. By calculating band-edge charge densities, electrostatic potentials, nonadiabatic couplings, and pure-dephasing times, we find that the lifetime variation is closely related to the built-in electric field and band-edge charge localization. The long lifetime in InAlS₃ originates from weak nonadiabatic coupling, whereas the short lifetime in Te-containing Janus layers is mainly attributed to enhanced nonadiabatic coupling between band-edge states. Our work reveals the microscopic mechanism of carrier recombination in five-atomic-layer Janus group-III chalcogenides and provides design principles for 2D Janus materials in photovoltaic and optoelectronic applications.